Rotary impact tool

ABSTRACT

The rotary impact tool has a hammer pin on the rotor which is self-unloading relieving the air pressure in the front end of the tool through a longitudinal exhaust passage in the rotor when the hammer pin is retracted, to prevent such air pressure from retarding the outward movement of the hammer pin in the next rotation of the rotor. A ball bearing in the tool supports the front end of the rotor for rotation and also guides the hammer pin in its movement laterally of the rotor, preventing the hammer pin from turning. This ball bearing is positively positioned by a cylindrical spacer whose opposite end engages another ball bearing which rotatably supports the anvil in the front end of the tool. Antifriction rollers are engaged between the anvil and the front end of the rotor to prevent side thrusts on the anvil from impeding the desired rotation of the rotor.

United States Patent [72] Inventor EarlG.Roggenburk 4120 Behrwald Ave., Cleveland, Ohio 44109 [2]] Appl. No. 636,528 [22] Filed May 5, 1967 [45] Patented Sept. 28, 1971 [54] ROTARY IMPACT TOOL 9 Claims, 5 Drawing Figs.

[52] U.S.Cl 173/93.5 [51] Int. Cl 525d 15/00 [50] Field of Search 173/93.5, 93.6 93 169 [56] References Cited UNITED STATES PATENTS 2,784,818 3/1957 Maurer 173/93.6 2,786,376 3/1957 Roggenburk.... l73/93.5 2,947,283 8/1960 Roggenburk.... 173/93.5 X 2,961,903 1 l/l Rogg enburk I N 173/93.5

3,106,274 10/1963 Madsen 173/93.6 3,181,672 5/1965 Swanson 173/93 3,323,395 6/1967 Burnett et a1 173/93 X Primary Examiner-David H. Brown Attorney-Ely, Golrick and Flynn ABSTRACT: The rotary impact tool has a hammer pin on the rotor which is self-unloading relieving the air pressure in the front end of the tool through a longitudinal exhaust passage in the rotor when the hammer pin is retracted, to prevent such air pressure from retarding the outward movement of the hammer pin in the next rotation of the rotor. A ball bearing in the tool supports the front end of the rotor for rotation and also guides the hammer pin in its movement laterally of the rotor, preventing the hammer pin from turning. This ball bearing is positively positioned by a cylindrical spacer whose opposite end engages another ball bearing which rotatably supports the anvil in the front end of the tool. Antifriction rollers are engaged between the anvil and the front end of the rotor to prevent side thrusts on the anvil from impeding the desired rotation of the rotor,

ROTARY IMPACT TOOL This invention relates to a fluid motor-operated rotary impact tool, such as an impart wrench.

Various rotary impact tools have been proposed heretofore in which the rotor of an air motor in each of its successive rotations imparts an impact blow to an anvil. The present invention is directed to improvements in such a tool which over comes various practical difficulties and disadvantages encountered in the use of prior tools of this general type.

An object of this invention is to provide a novel and improved rotary impact tool having a self-unloading hammer pin on the rotor of the motor for engaging and then automatically disengaging the anvil when an impact blow is delivered from the rotor to the anvil.

Another object of this invention is to provide a novel and improved rotary impact tool having a centrifugally movable hammer pin on the rotor which is retracted inwardly by fluid pressure leakage from the motor after delivering an impact blow to the anvil and which, when so retracted, relieves this leakage fluid pressure so that it does not retard the next outward movement of the hammer pin for imparting the next impact blow.

Another object of this invention is to provide a novel and improved rotary impact tool having an antifriction bearing which supports the front end of the rotor for rotation and also guides the hammer pin in its movement laterally of the rotor, preventing the hammer pin from turning.

Another object of this invention is to provide in a rotary impact tool a novel arrangement for positively locating the antifriction bearing which guides the hammer pin in its movement laterally of the rotor.

Another object of this invention is to provide a novel and improved rotary impact tool in which the striking surfaces of the hammer pin and the anvil are air-cooled and lubricated.

Another object of this invention is to provide a novel and improved rotary impact tool in which an antifriction bearing is engaged between the front end of the rotor and the anvil so that laterally directed load forces on the anvil do not impede the rotation of the rotor in the desired manner.

In the preferred embodiment of the present invention, a rotary fluid-operated impact tool is provided which has a separately formed massive end head mounted on the rotor to enhance the impact blow, preferably by being force fitted on the rotor to circumferentially overlie the outside of vane slots on the rotor at one end of these slots. A centrifugally slidable hammer pin on the rotor closes off an air passage in the rotor when the hammer pin is laterally outward and it vents this passage to the atmosphere when the hammer pin is laterally inward on the rotor, so that the next outward movement of the hammer pin will not be retarded. The front end of the rotor is rotatably supported by an antifriction bearing which also guides the hammer pin in its lateral movement, preventing the hammer pin from turning. This bearing is positively located axially, preferably by means of a spacer sleeve engaged between this bearing and another antifriction bearing which rotatably supports the anvil of the tool.

Further objects and advantages of this invention will be apparent from the following detailed description of a presently preferred embodiment thereof, which is illustrated in the accompanying drawing.

In the drawing:

FIG. 1 is a longitudinal sectional view of a rotary impact tool in accordance with the present invention;

FIG. 2 is a fragmentary longitudinal section of the front end of this tool, showing the hammer pin retracted laterally inward on the rotor;

FIG. 3 is a fragmentary horizontal section of the front end of the rotor, taken along the line 3-3 in FIG. 1;

FIG. 4 is a fragmentary vertical section through the front end of the rotor and the hammer pin, taken along the line 44 in FIG. 1, with the hammer pin engaging the anvil to impart rotation from the rotor to the anvil; and

FIG. 5 is a view similar to FIG. 4, but with the hammer pin retracted laterally inward on the rotor to ride over the anvil.

Referring first to FIG. 1, the impact tool of the present invention comprises a housing having an integral handle 11 to be held by the user and an end cap 12 which is bolted to the housing proper. Immediately to the left of the end cap 12 the housing 10 defines a cylindrical recess 8 which snugly receives a stationary two-piece liner, composed of an outer liner member 9 and a thin cylindrical inner liner member 13. The outer liner member 9 has a radial wall thickness which varies progressively from a maximum at the bottom in FIG. 1 to a minimum at the top, so that the cylindrical inner liner member 13 is supported offcenter with respect to the housing recess 8.

The relatively massive rotor 14 of an air motor is mounted for rotation about an axis which coincides with that of the housing recess 8 and which, therefore, is eccentric with respect to the inner liner member 13. This rotor has a plurality of radially, outwardly extending circumferentially spaced vane slots 15 which slidably receive respective vanes 16. When the rotor rotates, the vanes 16 move radially outward due to centrifugal force and their outer edges slidably engage the inside surface of the stationary liner member 13.

A stationary end plate 17 within the housing is engaged axially between the end cap 12 and the right end of the two-piece liner 9, 13 in FIG. 1. A ball bearing assembly 18 is engaged between the end plate 17 and the rotor 14 to support the latter for rotation with respect to the nonrotating end plate 17. The right end of the rotor projects axially beyond the ball bearing 18 into a recess 19 in the housing end cap 12. Within this recess a nut 20 is screw-threaded onto the end of the rotor, and a flat washer 21 is engaged between this nut and the inner race of the ball bearing 18.

At the right end of each vane slot 15 in FIG. 1, the rotor 14 presents a radial shoulder 22 which has a close running fit with the inner end face 17a of the end plate 17 and with an annular washer 23 which abuts against the inner race of the ball bearing 18.

Because of the eccentric position of the inner liner member 13 with respect to the rotational axis of the rotor, the vane 16 which is in a vane slot 15 facing downward toward the handle 11 is almost fully retracted within this vane slot, whereas the diametrically opposite vane has the maximum clearance from the bottom of the vane slot in which it is slidable. Between these two extremes, the rotor 14, vanes 16 and the inner liner 13 together define successive motor chambers of progressively increasing volume around the circumference of the rotor in both directions (clockwise and counterclockwise from the lower end of the inner liner member 13 to its upper end. If pressurized air is introduced into the group of motor chambers which increase in volume progressively from bottom to top in a clockwise direction (viewed from the end plate 12) and air is discharged from the remaining group of motor chambers from top to bottom in this clockwise direction, then the rotor will be driven clockwise, which is the forward" direction. Conversely, if pressurized air is introduced into the group of motor chambers which increase progressively in volume from bottom to top counterclockwise and air is discharged from the remaining motor chambers in this counterclockwise direction, the rotor will be driven counterclockwise, which is the reverse direction.

A valve arrangement is provided on the tool for operation selectively by the user to cause the air motor to operate either in the forward direction or in the reverse direction.

Referring to FIG. 1 at its lower end the outer liner member 9 has a longitudinal bore 25 which slidably receives a directional valve constituted by a spool valve member presenting a pair of longitudinally spaced cylindrical lands 26, 27 and a stem 28 connecting them. The lands have a sealing fit with the bore 25.

Liner member 9 has a forward" motor port 29 intersecting the bore 25 and communicating with a groove 30 in the inner liner member 13 which extends up circumferentially clockwise from port 29 around approximately a lower quadrant of the rotor 14. Groove 30 communicates directly with the space between the outside of the rotor 14 and the inside surface of the inner liner member 13 for almost half of the latter's circumferential extent clockwise upward from its lower end to supply pressurized air to the corresponding motor chambers to produce forward rotation of the rotor.

The outer liner member 9 also has a reverse" motor port 31 leading to a groove 32 in the inner liner member 13 which extends up circumferentially from port 31 counterclockwise around the opposite lower quadrant of the rotor 14. Groove 32 communicates directly with the space between the periphery of the rotor 14 and the inside surface of the inner liner member 13 for almost the remaining half of the latters circumferential extent to supply pressurized air to the corresponding motor chambers to produce reverse rotation of the rotor.

Approximately midway axially between the two motor ports 29 and 31 the outer liner member 9 at its lower end has an air inlet port 33 which communicates with a longitudinal passage 34 in the body through a port 35 in the latter.

As shown in FIG. 1, a coil spring 8 is engaged under compression between the spool valve and the housing end cap 12. This spring normally biases the spool valve to the FIG. 1 position, in which the inlet port 33 is in communication with the forward motor port 29, while the valve spool land 27 blocks the inlet port 33 from the reverse motor port 31.

The valve spool also has an intermediate position in which both motor ports 29 and 31 are closed by the respective valve spool lands 26 and 27.

Finally, the valve spool has a third position in which it is retracted to the right in FIG. 1, enough to connect the inlet port 33 to the reverse motor port 31, while the valve spool land 26 blocks the inlet port 33 from the forward motor port 29.

The left end of the spool valve is engaged by a pin 36, which is slidably disposed in a longitudinally extending opening 37 in the housing 10. This pin is attached to a reversing trigger member 38. This reversing trigger member carries a guide pin 39 extending parallel to and below the pin 36. The guide pin is slidably received in a bearing sleeve 40 carried by the housing 10. When the user grasps the reversing trigger member 38 with his index finger and retracts it fully to the right, the pin 36 forces the spool valve to the reverse position in which the inlet port 33 communicates with the reverse motor port 31.

The handle 11 of the tool has a vertical air inlet passage 41 which is screw-threaded at its lower end for connection to an air hose. A valve body 42 is mounted in the handle 11 at the upper end of this passage 41. This valve body has an external longitudinal groove which leads from passage 41 into a recess 44 in the handle. The valve body 42 has a longitudinal passage 45 whose right end opens into the handle recess 44. The opposite end of passage 45 communicates with a vertical passage 46 leading into the longitudinal passage 34 in the body 10.

An on-off valve poppet 47 within the handle recess 44 is positioned opposite the right end of a longitudinally extending stem 8. The opposite end of stem 48 is attached to a main trigger member 49, which is disposed outside the handle 11 in the path of the lower end of the reversing trigger member 38 when the latter is retracted. A coil spring 50 normally biases the valve 47 to the position shown in FIG. 1, in which it closes the passage 45 in the valve body 42 to prevent the flow of pressurized air from the inlet passage 41 in the handle into the valve body passage 45.

When the user retracts the main trigger 49 against the urging of spring 50, the valve member 47 is unseated and pressurized air can flow through the handle passages 41 and 46 to the inlet port 35 for the spool valve. Unless the reversing trigger member 38 is also retracted at this time, the valve spool will be in its forward position, as shown in FIG. 1, and the air motor will operate in the forward direction.

To operate the air motor in reverse, the user may retract the reversing trigger 38. In moving to the right, the reversing trigger engages and retracts the main trigger 49 to open the inlet valve 47, as well as retracting the spool valve 26-28 to the reverse position in which the inlet port 33 is connected to the reverse motor port 31 for operation of the air motor in the reverse direction.

The inner liner member 13 has a primary exhaust port 51 at its upper end which registers with an exhaust passage 52 in the outer liner member 9 leading to openings in the body 10 which pass the exhaust air to the exterior of the tool. The air trapped between successive vanes 16 on the rotor in the latter's rotation from the motor port 29 or 31 up to the exhaust port 51 is passed out of the motor.

The outer liner member 9 has a pair of circumferential grooves 53, 54 in its periphery which communicate with the reverse motor port 31 when the spool valve is positioned for forward rotation of the motor. These grooves 53, 54 lead to openings in the housing 10 for exhausting air from between the vanes on the rotor in its return travel from the upper end of the liner down to its lower end.

Similarly, the outer liner member 9 has a second pair of peripheral grooves 55, 56 which communicate with the forward motor port 29 when the spool valve is positioned for reverse rotation of the motor. These grooves 55, 56 lead to openings in the housing 10 for exhausting air from between the vanes on the rotor in its return travel from the upper end of the liner down to its lower end.

The housing 10 of the tool has a cylindrical bore 60 extending forward (to the left in FIG. 1) from the chamber 8 where the air motor is located. The rotor 14 has an integral extension 14a which projects into this housing bore 60.

A massive annular end head 61 is press fitted onto the rotor extension 14a to increase the effective mass of the rotor. The length of this end head 61 may be selectively varied so as to provide the total mass for the desired impact blow, as described hereinafter.

The right-end face of the end head 61 on the rotor abuts against the left end of the outer and inner liner members 9 and 13 and it is slidably engaged by the adjacent end faces of the vanes 16 in the air motor. The right end of the end head 61 overlies and provides a seal for the left end of each vane slot 15 in the rotor to minimize air leakage between the inlet and exhaust motor chambers in the air motor.

The periphery of the end head 61 on the rotor has a clearance in the housing bore 60, and pressurized air from the air motor can leak past the end head 61 into the interior of the housing to the left ofthe end head in FIG. 1.

The rotor extension 140 is supported for rotation by a ball bearing 62, comprising an outer race having a snug fit within the housing bore 60, an inner race on the rotor extension 140, and balls engaged between these outer and inner races. The right end of the inner race of bearing 62, abuts against a snap ring 63 on the rotor extension 14a.

The rotor extension 14a terminates in a reduced front end 64. A rotatable anvil 65 presents a rearwardly-facing central recess 66 into which the front end 64 of the rotor extends, with rollers 67 engaged between them to support the rotor for rotation with respect to the anvil. These rollers insure that laterally directed load forces on the anvil will not interfere with the desired rotation of the rotor.

A ball bearing 68 is engaged between the outside of the anvil 65 and the front end of the housing bore 60. The outer race of this bearing 68 has a snug fit inside the housing bore 60 and its front (left) end abuts against an integral front end wall 69 of the housing. A cylindrical spacer 70 is engaged axially between the outer races of the ball bearings 68 and 62. The inner race of bearing 68 is engaged axially between a snap ring 71 on the anvil 65 and an integral annular flange 72 on the back end of the anvil. The periphery of flange 72 has a running fit inside the spacer 70, and the spacer 70 preferably has a snug fit inside the housing bore 60. The anvil 65 has a reduced front end 73 projecting forward beyond the front end wall 69 of the housing for engagement with the tool (not shown) which is to be driven.

As best seen in FIGS. 4 and 5, the anvil 65 has an integral arcuate extension 74 extending rearward from its flange 72 and having a running fit inside the cylindrical spacer 70. As shown, this extension 74 has an arcuate extent of about 90.

The rotor extension 14a carries a radially movable hammer pin 75 for engagement with the anvil extension 74 to impart rotation from the rotor to the anvil 65 with an impact blow, as described hereinafter.

The rotor extension 14a has a radially extending recess 76 of circular cross section (FIG. 3) which slidably receives the inner end of the hammer pin 75. The rotor has a longitudinal passage 77 whose right end opens into the recess 19 in the housing end cap 12. The opposite end of passage 77 opens into a small radial bore 78 which intersects the radially inward end of the recess 76 and into a'slightly larger counterbore 79 which intersects the recess 76 radially outward beyond the longitudinal rotor passage 77. At the radially outward end of the counterbore 79 the rotor presents a shoulder 80 which terminates in an arcuate edge 81 that is part of the cylindrical wall of the recess 76. The hammer pin 75 when positioned radially outward, as shown in FIG. 1, has a cylindrical periphery which sealingly engages the sidewall of the recess 76 around its entire extent, including the arcuate edge 81. In accordance with an important feature of the present invention, the hammer pin coacts with this edge surface 81 to provide a valve for relieving the air pressure which retracts the hammer pin at the completion of an impact blow on the anvil 65, as described hereinafter.

The hammer pin has a reduced outer end 82 of square cross section (FIG. 3) whose corners are at the cylindrical periphery of the inner end of the hammer pin. This outer end 82 of the hammer pin presents a flat edge surface 83 at its right side which abuts against the inner race of the ball bearing 62 in all positions of the hammer pin radially of the rotor.

The rotor extension 14a has a longitudinal groove 90 in the bottom which passes air from the space between the end head 61 and bearing 62 into the space 84 which is bounded by the bearing 62, the flange 72 on the anvil and the spacer 70.

As shown in FIG. 2, when the hammer pin 75 is retracted radially inward, the space between the flat surface 83 on its reduced outer end 82 and the arcuate edge 81 on the rotor provides an air passage permitting the escape of air into the longitudinal rotor passage 77 from this space 84, and also from the space behind the bearing 62. At the opposite end of the longitudinal rotor passage 77, the recess 19 in the housing end cap communicates with a passage 85 (FIG. 1) in the end cap leading to the atmosphere. Consequently, every time the hammer pin 75 is retracted radially inward, air pressure in the space 84 is relieved to the atmosphere so as not to retard the next radially outward movement of the hammer pin.

At its radially inward end, the hammer pin 75 has a central recess 86 which snugly receives a resilient bumper 87 of rubber or rubberlike material. This bumper projects radially inward past the inner end of the hammer pin for engagement with the inner end wall 88 of the recess 76 in the rotor, when the hammer pin is retracted radially inward, to cushion the latter against shock.

In the operation of this tool, the air motor is driven by compressed air and, when the rotor 14 reaches the proper speed, the hammer pin 75 moves radially outward under the influence of centrifugal force. As the hammer pin revolves in unison with the rotor 14, it strikes one circumferential end of the anvil extension 74 (FIG. 4) a sharp blow, whose impact is enhanced by the heavy mass of the rotor 14 and the heavy end head 61, driving the anvil in the same rotational direction until the work load causes the air motor to stall, at which time the rotor rebounds slightly. At this time the air pressure in space 84 builds up to a value of several pounds per square inch, due to leakage from the air motor between the vanes 16 and the end head 61, around the end head 61 and through the ball bearing 62 into space 84. This air pressure forces the hammer pin radially inward until it clears the anvil extension 74, as shown in FIG. 5, at which time the rotor can resume its rotation. When the hammer pin is thus retracted radially inward by air pressure, it becomes unseated from the surface 81 on the rotor, as shown in FIG. 2, and permits the air pressure in chamber 84 to be exhausted to the atmosphere by way of the longitudinal rotor passage 77, the chamber in the housing end cap 12, and exhaust passage 85 in the end cap. The air expansion which takes place at this time cools the hammer pin 75 and the anvil extension 74.

If air tool oil or other suitable lubricant is introduced along with the pressurized air into the handle inlet passage 41, some of this lubricant will reach the space 84 where it will lubricate the striking surfaces of the hammer pin 75 and the anvil extension 74.

If the hammer pin 75 moves radially outward centrifugally when it is opposite the end of the anvil extension 74, it may strike a rounded corner of the anvil extension 74 at either circumferential end of the latter and rebound abruptly back into the recess 76 in the rotor. In such case, the force of such rebound is absorbed by the resilient bumper 87, which prevents breakage of the hammer pin or the rotor which might otherwise occur under these circumstances.

The spacer maintains the ball bearings 68 and 62 abutting against the respective snap rings 71 and 63 on the rotor. This insures the proper axial positioning of the bearing 62 so that the outer end 82 of the hammer pin will have sufficient clearance to move outward and inward radially. The flat face 83 on the outer end of the hammer pin has a running clearance with the inner race of the ball bearing 62 so as to prevent the hammer pin from turning about its own axis.

The rollers 67 prevent any lateral thrust which may be imparted to the anvil 65 from interfering with the rotation of the rotor 14.

While a presently preferred embodiment of the invention has been described in detail with reference to the accompanying drawing, it is to be understood that various modifications, omissions and refinements which depart from the disclosed embodiment may be adopted without departing from the spirit and scope of the present invention.

I claim:

1. A rotary impact tool comprising a housing, a rotary air motor in said housing, said housing having a chamber therein which is exposed to air pressure from said motor, said motor having a rotor with a passage therein which is vented to the atmosphere, a rotatable anvil having an extension disposed within said housing chamber, said rotor having a laterally disposed recess therein which is open to said rotor passage and whose outer end opens into said chamber, a hammer pin slidably mounted in said recess for centrifugal movement laterally outward into said chamber to strike said anvil extension an impact blow for imparting rotation from the rotor to the anvil, means to cause said hammer pin sealingly to engage the rotor at said laterally disposed recess therein to block said chamber from said rotor passage when the hammer pin is laterally outward on the rotor, and means to cause said hammer pin when retracted laterally inward into said recess to connect said chamber to said rotor passage to vent the air pressure in said chamber to the atmosphere through said rotor passage.

2. A rotary impact tool according to claim 1, and further comprising antifriction bearing means engaged between said rotor and said anvil.

3. A rotary impact tool according to claim 1, wherein said anvil has a rearwardly-facing recess therein at said housing chamber, said rotor has its front end projecting into said recess in the anvil, and further comprising antifriction rollers in said recess in the anvil rotatably supporting the front end of the rotor.

4. A rotary impact tool according to claim 1, wherein said hammer pin has an inner end slidably received in said laterally disposed recess in the rotor and an outer end of reduced cross section, said rotor at the outer end of said recess presenting a valve seat surface disposed between said chamber and said rotor passage, said hammer pin when positioned laterally outward on the rotor having its inner end sealingly engaging said valve seat surface to block the flow of air from said chamber into said rotor passage, and said hammer pin when retracted laterally inward on the rotor having its reduced outer end in spaced confronting relationship to said valve seat surface to permit pressurized air to flow from said chamber past said valve seat surface into said rotor passage to be vented to the atmosphere.

5. A rotary impact tool according to claim 4, and further comprising an antifriction bearing within the housing rotatably supporting the rotor, and wherein said reduced outer end of the hammer pin has a surface thereon which slidably engages one axial end of said bearing in all lateral positions of the hammer pin on the rotor to prevent the hammer pin from turning.

6. A rotary impact tool according to claim 5, and further comprising an additional antifriction bearing in said housing rotatably supporting said anvil, and a spacer engaged axially between said antifriction bearings to position said first-mentioned antifriction bearing for sliding engagement by the hammer pin in its movement laterally of the rotor.

7. A rotary impact tool comprising a housing, a rotary air motor in said housing having a rotor, a rotatably anvil, a hammer pin slidably mounted on said rotor for centrifugal movement laterally outward to strike said anvil for imparting rotation to the latter from the rotor, an antifriction bearing within said housing rotatably supporting the rotor, and means positioning said bearing at one axial side of said hammer pin for sliding engagement by the latter to guide the hammer pin in its movement laterally of the rotor.

8. A tool according to claim 7, wherein said housing has a chamber which is exposed to air pressure from said motor and into which said hammer pin extends laterally, said rotor has a passage which is vented to the atmosphere, said rotor has a valve surface between said housing chamber and said rotor passage, said hammer pin is sealingly engageably with said valve surface to block said rotor passage from said housing chamber when the hammer pin is laterally outward on the r0- tor, and said hammer pin is spaced from said valve surface to relieve the air pressure from said housing chamber into said rotor passage when the hammer pin is retracted laterally into the rotor.

9. A rotary impact tool according to claim 7, and further comprising an antifriction bearing within said housing rotatably supporting said anvil at the front of said rotor, and wherein said means positioning the bearing which rotatably supports the rotor includes a spacer engaged axially between said bearings. 

1. A rotary impact tool comprising a housing, a rotary air motor in said housing, said housing having a chamber therein which is exposed to air pressure from said motor, said motor having a rotor with a passage therein which is vented to the atmosphere, a rotatable anvil having an extension disposed within said housing chamber, said rotor having a laterally disposed recess therein which is open to said rotor passage and whose outer end opens into said chamber, a hammer pin slidably mounted in said recess for centrifugal movement laterally outward into said chamber to strike said anvil extension an impact blow for imparting rotation from the rotor to the anvil, means to cause said hammer pin sealingly to engage the rotor at said laterally disposed recess therein to block said chamber from said rotor passage when the hammer pin is laterally outward on the rotor, and means to cause said hammer pin when retracted laterally inward into said recess to connect said chamber to said rotor passage to vent the air pressure in said chamber to the atmosphere through said rotor passage.
 2. A rotary impact tool according to claim 1, and further comprising antifriction bearing means engaged between said rotor and said anvil.
 3. A rotary impact tool according to claim 1, wherein said anvil has a rearwardly-facing recess therein at said housing chamber, said rotor has its front end projecting into said recess in the anvil, and further comprising antifriction rollers in said recess in the anvil rotatably supporting the front end of the rotor.
 4. A rotary impact tool according to claim 1, wherein said hammer pin has an inner end slidably received in said laterally disposed recess in the rotor and an outer end of reduced cross section, said rotor at the outer end of said recess presenting a valve seat surface disposed between said chamber and said rotor passage, said hammer pin when positioned laterally outward on the rotor having its inner end sealingly engaging said valve seat surface to block the flow of air from said chamber into said rotor passage, and said hammer pin when retracted laterally inward on the rotor having its reduced outer end in spaced confronting relationship to said valve seat surface to permit pressurized air to flow from said chamber past said valve seat surface into said rotor passage to be vented to the atmosphere.
 5. A rotary impact tool according to claim 4, and further comprising an antifriction bearing within the housing rotatably supporting the rotor, and wherein said reduced outer end of the hammer pin has a surface thereon which slidably engages one axial end of said bearing in all lateral positions of the hammer pin on the rotor to prevent the hammer pin from turning.
 6. A rotary impact tool according to claim 5, and further comprising an additional antifriction bearing in said housing rotatably supporting said anvil, and a spacer engaged axially between said antifriction bearings to position said first-mentioned antifriction bearing for sliding engagement by the hammer pin in its movement laterally of the rotor.
 7. A rotary impact tool comprising a housing, a rotary air motor in said housing having a rotor, a rotatable anvil, a hammer pin slidably mounted on said rotor for centrifugal movement laterally outward To strike said anvil for imparting rotation to the latter from the rotor, an antifriction bearing within said housing rotatably supporting the rotor, and means positioning said bearing at one axial side of said hammer pin for sliding engagement by the latter to guide the hammer pin in its movement laterally of the rotor.
 8. A tool according to claim 7, wherein said housing has a chamber which is exposed to air pressure from said motor and into which said hammer pin extends laterally, said rotor has a passage which is vented to the atmosphere, said rotor has a valve surface between said housing chamber and said rotor passage, said hammer pin is sealingly engageably with said valve surface to block said rotor passage from said housing chamber when the hammer pin is laterally outward on the rotor, and said hammer pin is spaced from said valve surface to relieve the air pressure from said housing chamber into said rotor passage when the hammer pin is retracted laterally into the rotor.
 9. A rotary impact tool according to claim 7, and further comprising an antifriction bearing within said housing rotatably supporting said anvil at the front of said rotor, and wherein said means positioning the bearing which rotatably supports the rotor includes a spacer engaged axially between said bearings. 